Paraffins and olefins are the product of such methods as fluid catalytic cracking, MTBE etherification, or olefin isomerization. Production of highly branched hydrocarbons such as trimethylpentanes is important by virtue of their use as gasoline blending components high octane number. Traditional production of highly branched hydrocarbons is by condensation of isobutane with light olefins, usually butenes but sometimes mixtures of propene, butenes and possibly pentenes, using large quantities of conventional strong liquid acid catalysts, such as hydrofluoric or sulphuric acids. A mixture of immiscible acid and hydrocarbon is agitated to itiix the catalyst and reactant and refrigerated to control the highly exothermic reaction. By fine control of a complex interrelation of process variables, high quality alkylate production is maintained. The acid is recycled after use. It is desirable to use a process which is less hazardous and environmentally more acceptable.
Processes have been proposed to overcome these problems by using solid acids as catalysts. However paraffin-olefin condensation yields both desired alkylate and undesired oligomerization product. When catalyzing alkylation with solid acids it has been found tilat the selectivity for alkylate over oligomerization product is less than that obtained with liquid acids. Moreover, oligomerization products are thought to cause the observed progressive deactivation of the catalyst. Regeneration techniques are known for removing hydrocarbonaceous deposits from solid catalysts and restoring catalyst activity. Nevertheless, the known regeneration techniques are typically not totally satisfactory. One technique, for example, is raising the catalyst to elevated temperatures and oxidizing the deposits. For this method the alkylation must be interrupted and reactor conditions altered which causes lost production time.
In U.S. Pat. No. 3,706,814 a process is disclosed for alkylation of isoparaffins using acidic zeolite catalysts and supplying to the reactor paraffin and olefin in a volume ratio of from 15 to 30, the concentration of unreacted olefin in the reactor being maintained at less than 12 mole percent. Specifically the process is operated in a continuous stirred reactor using a zeolite Y catalyst. However, the experimental results in the '814 patent indicated severe deactivation occured even at low catalyst ages.
In the process of French patent No. 2,631,956, isobutane and butene are reacted over zeolite-beta catalyst in an upflow fixed bed reactor. Product analysis at 1 hour and 4 hours time on stream shows a decrease in the percentage olefin conversion level in the reactor with time on stream.
It would be advantageous to have an alkylation process which selectively yields highly branched alkylate at an acceptable rate for prolonged periods on stream.